The present invention relates to a control valve for controlling the displacement of a variable displacement compressor that is used in a vehicular air-conditioner.
A typical variable displacement compressor (hereinafter, referred to as a compressor) used in a vehicular air-conditioner includes a clutch mechanism, such as an electromagnetic clutch, on a power transmission path between an external drive source of the air-conditioner, which is the engine of the vehicle, and the compressor. When refrigeration is not needed, the electromagnetic clutch is turned off to discontinue power transmission from the engine to the compressor, thereby deactivating the compressor.
Turning on and off the electromagnetic clutch generates a shock, which lowers the engine performance of the vehicle. Therefore, clutchless type compressors are now widely being used. In a clutchless type compressor, the clutch mechanism, such as an electromagnetic clutch, is not arranged on the power transmission path between the engine and the compressor.
The clutchless type compressors use swash plate type variable displacement compressors. A swash plate type variable displacement compressor varies displacement in accordance with changes in the pressure in a crank chamber, which accommodates a swash plate. The pressure in the crank chamber of such compressor is controlled by adjusting the opening degree of a control valve, which is located in the compressor. The compressor includes a shutter, which is arranged in a discharge passage. The discharge passage connects a discharge chamber to an external refrigerant circuit. When the displacement of the compressor is minimized and the pressure acting on the discharge chamber side of the shutter decreases, the shutter mechanically detects the decrease and closes the discharge passage.
When refrigeration is not needed, the control valve minimizes the displacement of the compressor, thereby minimizing the power loss of the engine. In addition, the shutter prevents the refrigerant gas from being discharged to the external refrigerant circuit. This substantially stops the function of the compressor.
However, the control valve for controlling the displacement and the shutter for selectively opening the discharge passage are independently arranged in the compressor. This increases the number of parts forming the compressor, which increases the manufacturing cost of the compressor.
Accordingly, it is an objective of the present invention to provide a control valve that has some functions in addition to controlling the displacement of a variable displacement compressor to reduce the manufacturing cost of the compressor.
To achieve the above objective, the present invention provides a control valve for controlling the displacement of a variable displacement compressor that is incorporated in a refrigerant circuit. The compressor includes a control pressure chamber. The displacement of the compressor varies in accordance with the pressure in the control pressure chamber. The control valve includes a first valve body, a pressure sensing member, an actuator, and a second valve body. The first valve body varies the valve opening to adjust the pressure in the control pressure chamber. The pressure sensing member is displaced in accordance with the pressure in the refrigerant circuit to move the first valve body such that the displacement of the compressor is controlled to cancel the fluctuation of the pressure in the refrigerant circuit. The actuator urges the pressure sensing member by a force that corresponds to an external command to determine a target value of the pressure in the refrigerant circuit. The second valve body is operably coupled to the pressure sensing member. The second valve body adjusts the opening degree of a refrigerant passage, which forms a part of the refrigerant circuit, in accordance with the displacement of the pressure sensing member.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.